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Date: Thu, 13 Aug 2009 12:27:35 -0400
From: Brian Haley <brian.haley@...com>
To: Jens Rosenboom <jens@...one.net>
CC: Linux Network Developers <netdev@...r.kernel.org>
Subject: Re: [RFC] ipv6: Change %pI6 format to output compacted addresses?
Jens Rosenboom wrote:
>> Anyways, can you try this patch, it's less than 40 new lines :)
>> It might be good enough, but could probably use some help.
>
> For a start, it didn't even compile. ;-)
It did on net-next-2.6 last night, weird.
> Here is a new version that also
> fixes
>
> - Leave %pi6 alone
> - Don't compress a single :0:
> - Do output 0
>
> The results and also the remaining issues can be seen with the attached
> test program, that also exposes a bug in glibc for v4-mapped addresses
> from 0/16.
>
> To fully conform to the cited draft, we would still have to implement
> v4-mapped and also check whether a second run of zeros would be longer
> than the first one, although the draft also suggests that operators
> should avoid using this kind of addresses, so maybe this second issue
> can be neglected.
Yes, the "compress the most zeros" would be harder, and require two
passes over the address. I had to cut corners somewhere :)
And regarding v4-mapped, the easy fix to that is just detect it and
call the IPv4 routine. The attached patch does that, but without the
::ffff:
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 756ccaf..5710c65 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -652,13 +652,53 @@ static char *ip6_addr_string(char *buf, char *end,
> u8 *addr,
> {
> char ip6_addr[8 * 5]; /* (8 * 4 hex digits), 7 colons and trailing
> zero */
> char *p = ip6_addr;
> - int i;
> + int i, needcolon = 0, printhi;
> + u16 *addr16 = (u16 *)addr;
> + enum { DC_START, DC_MIDDLE, DC_DONE } colon = DC_START;
> +
> + /* omit leading zeros and shorten using "::" */
>
> - for (i = 0; i < 8; i++) {
> - p = pack_hex_byte(p, addr[2 * i]);
> - p = pack_hex_byte(p, addr[2 * i + 1]);
> - if (!(spec.flags & SPECIAL) && i != 7)
> + if (!(spec.flags & SPECIAL)) {
> + for (i = 0; i < 8; i++) {
> + if (addr16[i] == 0 && addr16[i+1] == 0 && colon == DC_START) {
This will access the array out-of-bounds when i=7.
Another hack below.
-Brian
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 756ccaf..ba70f2a 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -647,25 +647,6 @@ static char *mac_address_string(char *buf, char *end, u8 *addr,
return string(buf, end, mac_addr, spec);
}
-static char *ip6_addr_string(char *buf, char *end, u8 *addr,
- struct printf_spec spec)
-{
- char ip6_addr[8 * 5]; /* (8 * 4 hex digits), 7 colons and trailing zero */
- char *p = ip6_addr;
- int i;
-
- for (i = 0; i < 8; i++) {
- p = pack_hex_byte(p, addr[2 * i]);
- p = pack_hex_byte(p, addr[2 * i + 1]);
- if (!(spec.flags & SPECIAL) && i != 7)
- *p++ = ':';
- }
- *p = '\0';
- spec.flags &= ~SPECIAL;
-
- return string(buf, end, ip6_addr, spec);
-}
-
static char *ip4_addr_string(char *buf, char *end, u8 *addr,
struct printf_spec spec)
{
@@ -688,6 +669,73 @@ static char *ip4_addr_string(char *buf, char *end, u8 *addr,
return string(buf, end, ip4_addr, spec);
}
+static char *ip6_addr_string(char *buf, char *end, u8 *addr,
+ struct printf_spec spec)
+{
+ char ip6_addr[8 * 5]; /* (8 * 4 hex digits), 7 colons and trailing zero */
+ char *p = ip6_addr;
+ int i, needcolon, printhi;
+ u16 *addr16 = (u16 *)addr;
+ u32 *addr32 = (u32 *)addr;
+ enum { DC_START, DC_MIDDLE, DC_DONE } colon = DC_START;
+
+ if (!(spec.flags & SPECIAL)) {
+ /* omit leading zeros and shorten using "::" */
+
+ /* v4mapped */
+ if ((addr32[0] | addr32[1] |
+ (addr32[2] ^ htonl(0x0000ffff))) == 0)
+ return ip4_addr_string(buf, end, &addr[12], spec);
+
+ needcolon = 0;
+ for (i = 0; i < 8; i++) {
+ if (addr16[i] == 0 && i < 7 && addr16[i+1] == 0 &&
+ colon == DC_START) {
+ colon = DC_MIDDLE;
+ continue;
+ }
+ if (colon == DC_MIDDLE) {
+ if (addr16[i] == 0)
+ continue;
+ colon = DC_DONE;
+ *p++ = ':';
+ *p++ = ':';
+ } else if (needcolon)
+ *p++ = ':';
+ printhi = 0;
+ if (addr[2 * i]) {
+ if (addr[2 * i] > 0x0f)
+ p = pack_hex_byte(p, addr[2 * i]);
+ else
+ *p++ = hex_asc_lo(addr[2 * i]);
+ printhi++;
+ }
+ /*
+ * If we printed the high-order bits we must print the
+ * low-order ones, even if they're all zeros.
+ */
+ if (printhi || addr[2 * i + 1] > 0x0f)
+ p = pack_hex_byte(p, addr[2 * i + 1]);
+ else
+ *p++ = hex_asc_lo(addr[2 * i + 1]);
+ needcolon++;
+ }
+ if (colon == DC_MIDDLE) {
+ *p++ = ':';
+ *p++ = ':';
+ }
+ } else {
+ for (i = 0; i < 8; i++) {
+ p = pack_hex_byte(p, addr[2 * i]);
+ p = pack_hex_byte(p, addr[2 * i + 1]);
+ }
+ }
+ *p = '\0';
+ spec.flags &= ~SPECIAL;
+
+ return string(buf, end, ip6_addr, spec);
+}
+
/*
* Show a '%p' thing. A kernel extension is that the '%p' is followed
* by an extra set of alphanumeric characters that are extended format
--
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